Featured Research

from universities, journals, and other organizations

Protein that keeps stem cells poised for action identified

Date:

December 28, 2009

Source:

Stanford University Medical Center

Summary:

Researchers have now identified a critical component, called Jarid2, of this delicate balancing act -- one that both recruits other regulatory proteins to genes important in differentiation and also modulates their activity to keep them in a state of ongoing readiness.

Share This

Like a child awaiting the arrival of Christmas, embryonic stem cells exist in a state of permanent anticipation. They must balance the ability to quickly become more specialized cell types with the cellular chaos that could occur should they act too early (stop shaking those presents, kids!). Researchers at the Stanford University School of Medicine have now identified a critical component, called Jarid2, of this delicate balancing act -- one that both recruits other regulatory proteins to genes important in differentiation and also modulates their activity to keep them in a state of ongoing readiness.

Related Articles

"Understanding how only the relevant genes are targeted and remain poised for action is a hot topic in embryonic stem cell research," said Joanna Wysocka, PhD, assistant professor of developmental biology and of chemical and systems biology. "Our results shed light on both these questions." Wysocka is the lead author of the research, which will be published in the Dec. 24 issue of Cell.

Jarid2 works through a protein complex called PRC2, for Polycomb Repressive Complex 2. PRCs keep genes quiet by modifying DNA packaging proteins called histones. It's not quite tying a string around a brown paper package, but the concept is similar: Wrapping DNA up neatly around the histones helps it all fit in the tiny space and keeps it out of commission until the appropriate time. That's because, when wrapped, genes can't be converted into proteins to do the work of the cell. PRC2 adds a molecular "Do not open until Christmas" tag to ensure the DNA stays wrapped until it's needed.

PRC2 is necessary to regulate the expression of developmentally important genes in many types of cells. But Wysocka and her colleagues wanted to know specifically how it worked in embryonic stem cells. When they looked in mouse embryonic stem cells, they found that nearly all PRC2 is bound to a protein called Jarid2, which is more prevalent in embryonic stem cells than in non-stem cells.

Jarid2 had been previously identified as a protein important during development. But its role in embryonic stem cells hadn't yet been addressed. The Stanford researchers found that together PRC2 and Jarid2 occupied specific stretches of histone-bound DNA in both mouse and human embryonic stem cells. When they reduced the amount of Jarid2 in the cells, PRC2 was less able to bind the DNA and the cell began to churn out the proteins before they were needed -- confirming Jarid2's importance in stem cell differentiation.

Surprisingly, though, the degree of modifications on the histones remained about the same, even though less PRC2 was bound to the DNA. This suggested that when PRC2 is bound to Jarid2, it puts fewer "don't open" tags on the histones.

"This was a crucial finding," said Wysocka, "because it shows that Jarid2 both recruits PRC2 to the DNA and modulates its ability to modify the histones." It also suggests that the Jarid2/PRC2 complex inhibits gene expression in other, as-yet-unidentified ways. Such fine-tuning of PRC2 activity, the researchers believe, allows the cell to carefully manage its degree of readiness for the subsequent unwrapping and expression of genes involved in differentiation of the embryonic stem cells into more specialized cells.

The researchers confirmed their findings in frog embryos, which are more easily studied at early stages of differentiation than are mouse embryos, by depleting Jarid2 expression. They found that embryos missing Jarid2 were unable to complete a critically important developmental step called gastrulation.

"It was just as we would have predicted," said Wysocka. "Without Jarid2, which keeps the genes silent yet poised for activation, the embryos stop developing." The researchers now plan to further investigate the mechanism by which Jarid2 summons PRC2 to differentiation-specific genes in the stem cells, and how it affects gene expression. The interaction may be important in human cancers as well. "PRC2 is upregulated in some cancers," noted Wysocka, "which may help keep these cells in an undifferentiated, rapidly proliferating state. It will be interesting to see whether Jarid2 is also expressed at high levels in these diseases. There are all sorts of implications for stem cell biology, differentiation and human disease."

In addition to Wysocka, other Stanford scientists involved in the research include postdoctoral scholars Jamy Peng, PhD, and Anton Valouev, PhD; senior research scientist Tomek Swigut, PhD; and associate professor of pathology and of genetics Arend Sidow, PhD.

The research was supported by the California Institute for Regenerative Medicine, the W.M. Keck Distinguished Young Scholar and Searle Scholar Awards, the American Cancer Society and the National Institutes of Health.

Mar. 31, 2015  Increasing state alcohol taxes could prevent thousands of deaths a year from car crashes, say researchers, who found alcohol-related motor vehicle crashes decreased after taxes on beer, wine and ... full story

Mar. 31, 2015  Alcoholism takes a toll on every aspect of a person's life, including skin problems. Now, a new research report helps explain why this happens and what might be done to address it. "The clinical ... full story

Mar. 31, 2015  A new population of 'memory' immune cells has been discovered by scientists, throwing light on what the body does when it sees a microbe for the second time. This insight, and others like it, will ... full story

Mar. 31, 2015  Coronary heart disease and stroke, two of the leading causes of death in the United States, are diseases associated with heightened platelet reactivity. A new study in humans suggests an underlying ... full story

Mar. 31, 2015  A new study had researchers seeking answers to why the therapeutic benefit afforded by SSRIs was so limited in children and teenagers. If researchers can uncover the biological mechanisms preventing ... full story

Mar. 31, 2015  A drug being developed to treat osteoporosis may also be useful for treating osteogenesis imperfecta or brittle bone disease, a rare but potentially debilitating bone disorder that that is present ... full story

Mar. 31, 2015  It is possible to quantify and classify the effects of different diseases on the activity of intestinal bacteria, new research demonstrates for the first time. Human intestinal flora, known as ... full story

Mar. 31, 2015  During prenatal development, the brains of most animals, including humans, develop specifically male or female characteristics. But scientists have known little about the details of how this ... full story

Mar. 31, 2015  A history of depression may put women at risk for developing diabetes during pregnancy, according to research. This study also pointed to how common depression is during pregnancy and the need for ... full story

Featured Videos

Solitair Device Aims to Takes Guesswork out of Sun Safety

Reuters - Innovations Video Online (Mar. 31, 2015)  The Solitair device aims to take the confusion out of how much sunlight we should expose our skin to. Small enough to be worn as a tie or hair clip, it monitors the user&apos;s sun exposure by taking into account their skin pigment, location and schedule. Matthew Stock reports.
Video provided by Reuters

Soda, Salt and Sugar: The Next Generation of Taxes

Washington Post (Mar. 30, 2015)  Denisa Livingston, a health advocate for the Dinι Community Advocacy Alliance, and the Post&apos;s Abby Phillip discuss efforts around the country to make unhealthy food choices hurt your wallet as much as your waistline.
Video provided by Washington Post

S. Leone in New Anti-Ebola Lockdown

AFP (Mar. 28, 2015)  Sierra Leone imposed a three-day nationwide lockdown Friday for the second time in six months in a bid to prevent a resurgence of the deadly Ebola virus. Duration: 01:17
Video provided by AFP

Related Stories

Mar. 9, 2015  A regulatory protein involved in controlling how cancer spreads through the body also influences the fate of stem cells in the intestine of mice, and international team of researchers reports. The ... full story

Feb. 7, 2013  A single embryonic stem cell can develop into more than 200 specialized cell types that make up our body. This maturation process is called differentiation and is tightly regulated. New research has ... full story

Feb. 1, 2012  Researchers have determined the critical role one enzyme, lysine-specific demethylase 1 (LSD1), plays as mouse embryonic stem cells (ESCs) differentiate. This research may provide targets for ... full story

June 11, 2010  The mechanism by which "polycomb" proteins critical for embyronic stem cell function and fate are targeted to DNA has been identified by scientists in the UK. The discovery has implications ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.